Columnar structured material and method of manufacturing the same

ABSTRACT

A method of manufacturing a dot pattern includes the steps of preparing a structured material composed of a plurality of columnar members containing a first component and a region containing a second component different from the first component surrounding the columnar members, with the structured material being formed by depositing the first component and the second component on a substrate, and removing the columnar members from the structured material to form a porous material having a columnar hole. In addition, a material is introduced into the columnar hole portions of the porous material to form a dot pattern, and the porous material is removed.

This is a continuation of application Ser. No. 10/535,452, filed on May19, 2005, which is a National stage application of PCT/JP2003/015950,filed Dec. 12, 2003.

TECHNICAL FIELD

The present invention relates to a columnar structured material having amicrostructure and a method of manufacturing the same. Moreparticularly, the invention relates to a columnar structured materialmanufacturing method with which columnar portions of a columnarstructured material each having an extremely minute diameter and havinga uniform size can be formed and arranged on a substrate at extremelynarrow intervals. In particular, the invention contributes to achievingenhanced functions and performances of electronic devices and opticaldevices both utilizing quantum effect.

BACKGROUND ART

A so-called “low dimensional quantum structure”, in which amicrostructure of a semiconductor having a narrow band gap is surroundedin a two-dimensional or three-dimensional manner by a semiconductorhaving a wide band gap, is regarded as promising for achieving enhancedfunctions and performances of optical devices and electronic devices,and recently has been attracting an increasing interest as a key for thefuture development of the optical and electronic industries. Inparticular, since a quantum dot as a three-dimensional quantum enclosingstructure exhibits a remarkable quantum effect in a wide variety ofapplications due to the sharpness of a state density based on the strongelectron-enclosing effect, realization of the quantum dot is anticipatedas a basic structure of the optical and electronic devices havingfunctions and performances superior to those of the prior art.

As for a technique for forming these microstructures, there is alithography technique utilizing an electron beam, an ion beam, or an STMneedle. In recent years, a fine patterning up to 100 nm or less hasbecome possible. However, these methods have such a disadvantage that amanufacturing cost is still high, and it takes a lot of time to carryout the processing. In addition, in order to further increase theenclosing effect, a structure having a size on the order of even smallerthan 100 nm is required.

In order to solve the above-mentioned problems, there has been proposeda method in which a substrate is selectively etched using a mask havinga microstructure to form a microstructured material. Since a largenumber of microstructured materials can be formed at a time by themethod using a mask, this method is very advantageous in terms ofprocessing time.

In JP 11-112099 A, there is disclosed a method in which first of all, amask material is deposited on a substrate with a porous material calleda trough hole membrance having a plurality of through holes as a mask, apattern of dots made of the mask material is formed, and the substrateis selectively etched with the dot pattern as a mask to form minuteprojections on a surface of the substrate.

In addition, in Journal of Applied Physics, Vol. 91, No. 9, 6057 (2002),there is reported a method in which a cluster of gold is formed on asurface of a substrate by utilizing nucleus portions of micelle formedfrom a diblock copolymer, and a pillar-like structured material ismanufactured with the cluster as a mask. In this case, it is describedthat a size of the mask, i.e., the cluster can be regulated by an amountof metallic salt dissolved in a diblock polymer solution, and intervalsof arrangement can be regulated by a molecular weight of a hydrophobicportion of the diblock polymer.

In these methods using a mask, it can be said that a size of amicrostructured material finally formed, and intervals of arrangementare substantially determined by a structure of the mask.

In JP 11-112099 A as well, a structure of the minute projections isdetermined by a structure of the through hole membrane serving as thefirst mask. The through hole membrane described in above-mentioned JP11-112099 A is formed such that another substrate having projectionsarranged at desired intervals is pressed against an aluminium substrateto form a minute depression pattern on the aluminium substrate, andnext, the aluminium substrate is subjected to anodic oxidation in anacid electrolytic solution to thereby form holes from the minutedepression portions. Accordingly, arrangement intervals of the minutedepressions can not be made equal to or smaller than the originalarrangement intervals of the projections on the other substrate, andhence it is conceivable that the practical limit of the arrangementintervals is of the order of several nanometers. In addition, although ahole diameter can be increased within a range not exceeding thearrangement intervals through an after-treatment, it is difficult tomake the hole diameter smaller. Hence, the hole diameter issubstantially of the order of several tens nano-meters in many cases.

However, it is said that if a size of a microstructure of asemiconductor is made about equal to or smaller than 20 nm, then adistribution of energies of the electrons or holes within the structurecan be made very narrow. For example, if a microstructure called aquantum fine line or a quantum dot is applied to a semiconductor laser,then it is possible to realize a semiconductor laser having an extremelylow threshold current. Accordingly, in order to realize such asemiconductor laser, there is required a technique for uniformly anddensely forming a structure having a shape of a size of the order ofeven smaller than several tens nano-meters mentioned above.

In addition, application of such a microstructured material to a singleelectron device such as a single electron transistor or a singleelectron memory is also anticipated. However, in many cases, such amicrostructured material exhibits its unique property such as a quantumsize effect only when its size becomes smaller than 10 nm. Accordingly,from the viewpoint of application to the single electron device as well,the realization of an ultra-micro structure is desired.

On the other hand, according to the report of Journal of AppliedPhysics, Vol. 91, No. 9, 6057 (2002), a pillar-like structured materialhaving a diameter equal to or smaller than 10 nm becomes possible.However, the arrangement intervals are regulated by a size of themicelle formed from the diblock polymer, and hence are about 100 nm. Forstable formation of the micelle, it is necessary to stably separate ahydrophobic portion and a hydrophilic portion of the diblock polymer. Inorder to attain this, a certain chain length is required for thehydrophobic portion and the hydrophilic portion within the polymer.Accordingly, there is actually a limit to shortening of the arrangementintervals by shortening of a chain length of the hydrophobic portion.Hence, it can be said that problems remain in achieving higher densityas mentioned above.

The present invention has been made in the light of the above-mentionedproblems, and it is therefore an object of the present invention toprovide a method of forming, on a substrate, columnar portions of acolumnar structured material each having an extremely minute size atminute intervals at a low cost and in a short period of time, and acolumnar structured material formed by utilizing the manufacturingmethod.

DISCLOSURE OF INVENTION

A method of manufacturing a mask member according to the presentinvention is characterized by including the steps of: preparing astructured material including a plurality of columnar members, and aregion surrounding the columnar members; removing the columnar membersfrom the structured material to form a porous material having columnarhole portions; and introducing a mask material into the columnar holeportions of the porous material.

Further, a mask member according to the present invention ischaracterized in that the mask member is obtained by introducing a maskmaterial into a porous material obtained by removing columnar membersfrom a structured material formed so as to include the columnar membersand a region surrounding the columnar members.

In this structure, it is preferable that columnar members formed so asto contain a first material are surrounded by the region formed so as tocontain a second material, and that the second material is contained ata ratio of not less than 20 atomic % and not more than 70-atomic % withrespect to the total amount of the first material and the secondmaterial.

In order to achieve the above-mentioned object, according to the presentinvention, there is provided a columnar structured material formed on asubstrate so as to have a columnar structure, characterized in that thecolumnar structure is formed through an etching process in which dotsare utilized as a mask on a substrate, the dots being made of a maskmaterial and obtained by removing a porous material after the maskmaterial is introduced into holes of the porous material having columnarholes formed by removing columnar substances from a structured materialin which the columnar substances formed so as to contain a firstcomponent are dispersed in a member formed so as to contain a secondcomponent that can form a eutectic together with the first component.

It is preferable that the structured material is formed of a thin film.

It is preferable that the columnar substance is made of aluminium andthe member is made of silicon, and wherein the ratio of silicon in thestructured material is in a range of not less than 20 atomic % and notmore than 70 atomic %. Alternatively, it is preferable that the columnarsubstance is made of aluminium and the member is made of germanium andwherein the ratio of germanium in the structured material is in a rangeof not less than 20 atomic % and more than 70 atomic %.

It is preferable that a main component of the porous material is siliconor germanium.

It is preferable that the diameter of the columnar structured materialis not smaller than 0.5 nm and not larger than 15 nm. It is preferablethat the interval between adjacent columnar portions of the columnarstructured material is not less than 5 nm and not larger than 20 nm.

It is preferable that the columnar substance is a crystalline substance,and the member is an amorphous substance.

It is preferable that the mask material forming the dots contains anoble metal, especially gold.

It is preferable that the columnar structured material is made of onelayer or a plurality of layers of materials and that at least one of theone layer or the plurality of layers of materials is a semiconductor.

Further, a method of manufacturing a columnar structured materialaccording to the present invention is characterized by including: a stepof preparing, on a substrate, a structured material in which columnarsubstances formed so as to contain a first component are dispersed in amember formed so as to contain a second component that can form aeutectic together with the first component; a removal step of removingthe columnar substances; an introducing step of introducing a maskmaterial into columnar holes of a porous material having the columnarholes obtained through the removal step; a step of preparing dots madeof the mask material by removing the member; a step of etching thesubstrate with the dots as a mask; and a step of removing the dots. Itis preferable that the removal step of removing the columnar substancesis an etching step.

It is preferable that the introducing step of introducing a maskmaterial into the holes is an electrodeposition step.

It is preferable that the step of etching the substrate with the dots asa mask is a dry etching step.

A structured material serving as a base material of the above-mentionedporous material will hereinbelow be described.

The structured material to which the present invention is applied is astructured material formed so as to contain the first component and thesecond component, and the columnar substances formed so as to containthe first component are surrounded by a member formed so as to containthe second component. In this structure, it is desirable that the secondcomponent be contained in the structured material at a ratio of not lessthan 20 atomic % and not more than 70 atomic % with respect to the totalamount of the first component and the second component.

The above-mentioned ratio means a ratio of an amount of the secondcomponent to the total amount of first component and second componentwhich constitute the above-mentioned structured material, and ispreferably not less than 25 atomic % and not more than 65 atomic %, andis more preferably not less than 30 atomic % and not more than 60 atomic%.

Note that, for the above-mentioned columnar substance, it suffices thata columnar shape is substantially realized. For example, the secondcomponent may be contained as a component of the columnar substance, orthe first component may be contained as a component of theabove-mentioned member. In addition, a small amount of element such asoxygen, argon, nitrogen, or hydrogen may be Contained in the columnarsubstance or in a member in the periphery of the columnar substance.

The above-mentioned ratio is obtained by carrying out a quantitativeanalysis utilizing an induction-coupled plasma emission spectrometrymethod for example.

As for the above-mentioned first and second components, materials havinga eutectic point in a component system phase equilibrium diagram of boththe materials (so-called eutectic system materials) are preferable. Inparticular, materials having a eutectic point equal to or higher than300° C., preferably equal to or higher than 400° C. are desirable. Notethat, as for a preferred combination of the first component and thesecond component, one in which Al is used as the first component and Siis used as the second component, one in which Al is used as the firstcomponent and Ge is used as the second component, or one in which Al isused as the first component and Si_(x)Ge_(1-x) (0<x<1) is used as thesecond component is preferable.

A planar shape of each column of the above-mentioned columnar substanceis a circular or elliptical shape. In the above-mentioned structuredmaterial, a plurality of the columnar substances are arranged in amatrix formed so as to contain the second component. A size of eachcolumnar substance (a diameter when the planar shape is a circle) can becontrolled mainly in accordance with the composition of theabove-mentioned structured material (i.e., a ratio of the secondcomponent). Its average diameter is not smaller than 0.5 nm and notlarger than 50 nm, preferably not smaller 0.5 nm and not larger than 20nm, and more preferably not smaller than 0.5 nm and not larger than 15nm. In the case of an ellipse, it suffices that a length of the largestouter diameter portion falls within the above-mentioned range. Here, theaverage diameter means a value which is directly derived from aphotograph of columnar portions observed from an actual SEM picture (ina range of about 100 nm×about 70 nm), or indirectly derived byimage-processing the SEM picture with a computer. A practical lowerlimit of the average diameter is not smaller than 1 nm and not largerthan several nano-meters.

In addition, a center-to-center distance 2R between the plurality ofcolumnar substances is not smaller than 2 nm and not larger than 30 nm,preferably not smaller than 5 nm and not larger than 20 nm, and morepreferably not smaller than 5 nm and not larger than 15 nm. Of course,the above-mentioned distance 2R as a lower limit of the center-to-centerdistance has to have at least such an interval that does not cause thecolumnar substances to come into contact with each other.

The above-mentioned structured material is preferably a film-likestructured material. In such a case, the above-mentioned columnarsubstances are dispersed in a matrix formed so as to contain the secondcomponent in such a manner as to be substantially perpendicular to anintra-face direction of the film. While a thickness of the film-likestructured material is not particularly limited, a range of 1 nm to 100μm may be applied. Considering a process time and the like, a morerealistic film thickness falls within a range of about 1 nm to about 1μm. In particular, it is preferable that the columnar structure bemaintained even with a thickness equal to or larger than 300 nm.

The above-mentioned structured material is preferably a film-likestructured material. In this case, the structured material may beprovided on a substrate. While the substrate used is not particularlylimited, an insulating substrate such as a quartz glass substrate, asemiconductor substrate such as a silicon substrate, a gallium arsenidesubstrate or an indium phosphorus substrate, or a metallic substratesuch as an aluminium substrate, or, as long as the above-mentionedstructured material can be formed on the substrate as a supportingmember, a flexible substrate (e.g., a polyimide resin substrate) can beused.

The above-mentioned structured material can be formed by utilizing amethod of forming a film in a non-equilibrium state. As for the filmforming method concerned, a sputtering method is preferable. However,there can be adopted an arbitrary film forming method in which asubstance is formed in a non-equilibrium state by various methods suchas a resistance heating vacuum evaporation method, an electron beamvacuum evaporation (EB vacuum, evaporation) method, or an ion platingmethod. In a case where the sputtering method is adopted for formationof the structured material, a magnetron sputtering method, an RFsputtering method, an ECR sputtering method, or a DC sputtering methodcan be used. Also, in the case where the sputtering method is used, afilm is formed while setting a pressure within a reactor to be within arange of about 0.2 to about 1 Pa in an atmosphere of argon gas. Whenperforming the sputtering, while the first material and the secondmaterial which were separately prepared may be used as a raw material ofa target, alternatively, a target material in which the first materialand the second material are previously baked at a desired ratio may alsobe used.

The above-mentioned structured material to be formed on a substrate isformed at a substrate temperature of not lower than 20° C. and nothigher than 300° C., preferably not lower than 20° C. and not higherthan 300° C.

The above-mentioned columnar substance is removed from theabove-mentioned structured material (by wet etching or dry etching) tothereby form a porous material having a plurality of columnar holes.When performing the etching, it suffices that the columnar member can beselectively removed. As for an etchant, an acid such as phosphoric acid,sulfuric acid, hydrochloric acid, or nitric acid is suitable. It issuitable that holes of a porous material formed through the removalprocess are not linked to one another, but are independent of oneanother.

A method of forming a porous material from the above-mentionedstructured material desirably includes the steps of: preparing astructured material formed so as to contain a first component and asecond component, with a columnar member formed so as to contain thefirst component being surrounded by a region formed so as to contain thesecond component, the second component being contained in the structuredmaterial at a ratio of not less than 20 atomic % and not more than 70atomic % with respect to the total amount of first component and secondcomponent; and removing the Columnar member from the structuredmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G are schematic cross sectional viewsshowing an example of a method of forming a Columnar structured materialaccording to an embodiment of the present invention;

FIG. 2 is a schematic view showing a structure of a film in which acolumnar substance according to the embodiment of the present inventionis formed;

FIG. 3 is a schematic view showing a structure of a porous filmaccording to the embodiment of the present invention;

FIG. 4 is a schematic view showing arrangement of a dot patternaccording to the embodiment of the present invention; and

FIGS. 5A and 5B are schematic cross sectional views showing a substrateand a columnar structured material according to Example 3 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a columnar structured material according to the presentinvention and a method of manufacturing the same will hereinafter bedescribed with reference to the accompanying drawings.

In this embodiment, a pattern of minute dots is formed using a novelporous film having an extremely minute hole diameter and extremelyminute intervals of arrangement of microholes as compared with aconventional porous material, and a columnar structured material havingan extremely minute structure is manufactured with the dot pattern usedas a mask.

Here, a description will now be given of the porous film according tothis embodiment.

When a film made of a plurality of substances forming a eutectic systemtogether is formed on a substrate by utilizing a sputtering method orthe like for example, components of these substances are presentindependently of one another in the film without being mixed with oneanother. Then, in a case where film forming conditions and compositionof substances are optimized with respect to a specific material system,as shown in FIG. 2, a structure is formed in which a certain componentis dispersed to be present in a matrix 23 of other component in the formof a column having a minute diameter, i.e., a columnar substance 22.This structure is a novel structure discovered by the present inventors.The columnar substances are present so as to completely extend from aninterface of a substrate 21 to a surface of a film. A diameter of onecolumn of the formed columnar substance is in a range of 0.5 to 15 nm.In addition, a center-to-center interval of the columnar substance is ina range of 5 to 20 nm.

Giving a description using a specific example, when a mixed film made ofaluminium and silicon is formed on a substrate by utilizing a sputteringmethod, if the conditions are optimized, then crystalline aluminiumcolumns are formed within a matrix made of amorphous silicon. A diameterof the formed aluminium column is in a range of 0.5 to 15 nm. It isshown from the observation using a scanning electron microscope thataluminium is present in the form of a single column so as to extend froman interface of a substrate to a surface of a film. The formation of thesame structure is verified as well with respect to a mixed film ofaluminium and germanium formed by utilizing a sputtering method. A filmthickness can be controlled by adjusting a sputtering time. Hence, evenif the thickness is increased, the formation of the columnar structureis not interrupted unless the sputtering is discontinued.

In this embodiment, a film which is obtained by removing the columnarsubstance from a film containing the columnar substance on a substrate31 is used as a porous film 33 as shown in FIG. 3, a substance servingas a material of a mask is introduced into microholes 32 of the porousfilm 33, and the porous film is then removed to thereby obtain a dotpattern 42 as shown in FIG. 4 on a substrate. Then, the substrate isselectively etched with the dot pattern used as a mask to form aplurality of columnar portions of a columnar structured material eachhaving an extremely minute structure simultaneously, i.e., in a shortperiod of time.

Next, a description will hereinbelow be given with respect to amanufacturing method according to this embodiment.

Columnar portions of a columnar structured material each having anextremely minute diameter can be formed at extremely minute intervals ona substrate through the following processes (A) to (D). FIG. 1 areschematic cross sectional views showing a method of manufacturing acolumnar structured material according to this embodiment.

Process (A): Preparation of Substrate

First of all, as shown in FIG. 1A, a substrate 11 is prepared. Thesubstrate 11 is not basically intended to be limited in terms ofmaterial and thickness. Hence, various kinds of materials such as glass,a metal, ceramics, a semiconductor, and an organic substance can be usedfor the substrate 11. The substrate 11 may be formed of a bulk materialin which the substrate itself becomes a columnar structured material, ora material layer (columnar structured material formation layer) servingas a columnar structured material may be formed on a surface of a basesubstrate. In this embodiment, a substrate as a bulk material, and asubstrate structure having a columnar structured material formationlayer formed on a surface of a base substrate are collectively referredto as a substrate.

While a semiconductor such as GaAs or InAs is a useful material for thesubstrate 11 from a viewpoint of application to optical devices andelectronic devices, a material of the substrate 11 is not intended to belimited to such a semiconductor. A layer having a multiple quantum wellstructure including two or more layers such as AlGaAs/GaAs orGaAs/InGaAs may be formed as a columnar structured material formationlayer on a surface of a base substrate in correspondence to a structureof a desired microstructured columnar structured material. In addition,this columnar structured material formation layer may be formed byutilizing an existing method such as a molecular beam epitaxial growthmethod (MBE method).

Process (B): Formation of Porous Film

Next, a detailed description will hereinbelow given with respect to amethod of forming a porous film 15 having microholes 14 as shown in FIG.1C on the substrate 11.

As shown in FIG. 1B, a thin film having a structure in which columnarsubstances 12 as a first component of a columnar form are dispersed in amatrix 13 made of the other component is formed on the substrate 11 byutilizing a sputtering method using a target containing materialsforming a eutectic system together in a suitable ratio. In this case,the used target does not need to be made of a mixed substance of twocomponents. Hence, a material in which one substance is placed on theother substance may also be used as the target, or a material having astructure in which two substances are stuck on each other so as to givea desired area ratio may also be used.

Giving an exemplification, the sputtering is carried out in a state inwhich a suitable number of silicon wafers are placed on an aluminumtarget, whereby a film having the above-mentioned structure can beformed on the substrate 11.

The formation of a film is described by giving the sputtering method asan example. However, any film formation method can be applied to thepresent invention as long as the same structure is formed.

The average diameter 2r of the formed columnar substance 12 is in arange of 0.5 to 15 nm. In addition, the average center-to-centerinterval 2R of the columnar substance 12 is in a range of 5 to 20 nm(see FIG. 1B).

Next, as shown in FIG. 1C, the above-mentioned columnar substance 12 isselectively removed from the formed structure to form a porous film 15.The wet etching is preferably used for the selective removal of thecolumnar substance 12. For example, in the case of crystalline aluminiumcolumns formed in a matrix made of amorphous silicon, only thecrystalline aluminium columns can be etched away using phosphoric acidor sulfuric acid without changing the shape of silicon to thereby formmicroholes 14.

In addition, in order to simply carry out the subsequent processes, aprocess of subjecting the formed porous film 15 to a chemical processingto change the property of the porous layer may be carried out in somecases. More specifically, the chemical processing in this case means anoxidation processing or the like.

Process (C): Formation of Dot Pattern

Next, a description will hereinbelow be given with respect to a methodof forming a dot pattern 16 within the microholes 14 of the porous film15 as shown in FIG. 1D.

Any of metals such as Pt, Au, Ni, Al, or Ta, silicon oxide, siliconnitride or the like may be used as a material for the dot pattern. Thatis, any material may be used with which selectivity can be obtained withrespect to the substrate 11 during the etching, and which is not anobstacle to the subsequent processes. In addition, if the substrate 11has conductivity, then a metal or the like can be simply introducedthrough an electrodeposition process. Also, a substance serving as acatalyst may also be formed on bottoms of the microholes 14 through theelectrodeposition process to form an objective material with assistanceof the catalytic activity. Also, the catalyst to be formed on thebottoms of the microholes 14 may also be formed on the surface of thesubstrate 11 by utilizing the vapor deposition method or the like beforethe formation of the porous film 15.

In addition, an organic substance may also be used as a material for thedot pattern. An organic substance such as polyaniline iselectrolytically polymerized within holes of the porous layer to therebyallow an excellent mask pattern to be obtained.

A pattern 16 of dots made of an objective dot pattern material, as shownin FIG. 1D, is formed through the above-mentioned process in the matrix13 which surrounded the columns of the columnar substance 12 in theoriginal film.

Next, as shown in FIG. 1E, the porous film 15 is removed. In thisprocess, a structure is formed in which the porous film 15 isselectively removed so that only the dot pattern 16 is arranged on thesubstrate 11. FIG. 4 is a perspective view showing the dot pattern 16(designated by reference numeral 42 in the figure) formed on thesubstrate 11 (designated by reference numeral 41 in the figure) throughthis process.

As for a method of selectively removing the porous film 15, a processsuch as an etching process can be applied. For example, in a case wheresilicon is a material for an original porous film and changed to siliconoxide after being subjected to the chemical processing in the process(B), the etching using dilute hydrofluoric acid can be satisfactorilyapplied.

The dot pattern 16 is formed on the substrate 11 as shown in FIG. 1Ethrough the above-mentioned process C.

Process (D): Etching of Substrate

Next, as shown in FIG. 1F, the substrate 11 is selectively etched toform a columnar structured material 17 on the surface of the substrate11. Here, while for this etching process, the wet etching using an acidmay be used, the dry etching such as Ar ion milling etching or etchingusing reactive ions is more suitable. In particular, a reactive ion beametching method (RIBE) as a method of applying ions accelerated atseveral hundreds to several kilo-volts to a specimen by an ion gun toetch the specimen is suitable since a vertical processing can be carriedout with high accuracy.

Next, as shown in FIG. 1G, if the dot pattern 16 which is used as anetching mask is removed using a plasma oxidation processing, a suitableacid treatment (wet), or the like, then the columnar structured material17 made of a suitable material is obtained.

In addition, here, the formed columnar structured material 17 may besubjected to an annealing treatment to recrystallize the columnarstructured material 17.

In addition, if atoms, molecules, a reactive gas or the like are appliedto the holes of the columnar structured material 17 by utilizing anexisting crystal growth technique such as an MBE method or a metalorganic vapor phase epitaxial growth method (MOVPE), then a buried layercan be formed using any other material.

As described above, according to this embodiment, the novel porous filmhaving the extremely minute structure is formed from the film made of aplurality of substances forming a eutectic system together, thesubstance serving as the mask material is introduced into the microholesof the porous film, and the porous film is then removed to therebyobtain the dot pattern. Then, the substrate is selectively etched withthe dot pattern used as the etching mask to collectively form thecolumnar portions of the columnar structured material each having theextremely minute structure at the minute arrangement intervals.

Consequently, if the columnar structured material formed in accordancewith this embodiment is applied to a semiconductor laser for example,then it is possible to realize the promotion of high performance such asreduction of a threshold current, stabilization of characteristics, andenhancement of a gain. Moreover, the columnar structured material canalso be applied to an electronic device such as an operational element,and an optical device both utilizing the effect of enclosing theelectrons or light and the quantum effect, to thereby contribute topromotion of an excellent function and high performance of such devices.

EXAMPLES

The present invention will hereinbelow be described in detail withrespect to the following examples. However, the present invention is notintended to be limited to these embodiments, and hence materials,reactive conditions, and the like can be freely changed within a scopein which a Columnar structured material having the same structure can beobtained

Example 1 First Material Al, Second Material Si

In this example, there was obtained an aluminium microwire as a mixedfilm to be used as a host material of a porous film, in which analuminium structured material portion surrounded by silicon had acolumnar structure, a diameter 2r of 3 nm, an interval 2R of 7 nm, and alength L of 200 nm.

First, a description will be given of a production method for analuminium microwire.

An aluminium/silicon mixture film containing 55 atomic % of silicon withrespect to the total amount of aluminium and silicon was formed into athickness of approximately 200 nm on a glass substrate by RF magnetronsputtering. Used as the target was a 4-inch aluminium target on whicheight silicon chips 13 of 15 mm square were superposed. Sputteringconditions were set such that an RF power supply was used, an Ar flowrate of 50 sccm, a discharge pressure of 0.7 Pa, and a starting power of1 kW. Also, the temperature of the substrate was set to the roomtemperature.

Note that the aluminium target on which the eight silicon chips weresuperposed was used here as the target. However, the number of thesilicon chips is not limited thereto. The number changes depending onthe sputtering conditions, and may be any number as long as thecomposition of the aluminium/silicon mixture film is approximately 55atomic %. Also, the target is not limited to the aluminium target onwhich the silicon chips were superposed, and may be a silicon target onwhich aluminium Chips are superposed, or a target obtained by sinteringsilicon and aluminium powders.

Next, the aluminium-silicon mixture film obtained in this way wasanalyzed concerning the fractional amount of silicon (atomic %) withrespect to the total amount of aluminium and silicon through an ICP(induction-coupled plasma emission spectrometry). As a result, it wasfound that the fractional amount of silicon was about 55 atomic % withrespect to the total amount of aluminium and silicon. Note that for theconvenience of the measurement here, an aluminium-silicon mixture filmdeposited on a carbon substrate was used for a substrate.

The aluminium-silicon mixture film produced as described above wasobserved with an FE-SEM (field emission scanning electron microscope).As a shape of the surface viewed from directly above the substrate,circular aluminium nanostructured materials surrounded by silicon werearranged two-dimensionally. The hole diameter of the aluminiumnanostructured material parts was 3 nm, and the average center-to-centerinterval thereof was 7 nm. In addition, when the cross section thereofwas observed with the FE-SEM, the height of the film was 200 nm, and therespective aluminium nanostructured material parts were independent fromeach other.

Further, when this sample was observed by an X-ray diffraction method, apeak of silicon exhibiting crystallinity could not be confirmed and thesilicon was amorphous.

Accordingly, the aluminium/silicon nanostructured material could beproduced, which includes the aluminium microwire surrounded by siliconand having an interval 2R of 7 nm, a diameter 2r of 3 nm, and a length Lof 200 nm.

Comparative Example

As a comparative sample A of the example above, the aluminium/siliconmixture film containing 15 atomic % of silicon with respect to the totalamount of aluminium and silicon was formed on the glass substrate into athickness of approximately 200 nm by sputtering. Used as the target wasthe 4-inch aluminium target on which two silicon chips 13 of 15 mmsquare were superposed. The sputtering conditions were set such that theRF power supply was used, an Ar flow rate of 50 sccm, a dischargepressure of 0.7 Pa, and a starting power of 1 kW. Also, the temperatureof the substrate was set to the room temperature.

The comparative sample A was observed by FE-SEM (field emission scanningelectron microscope). With regard to the form of the surface viewed fromright above the substrate, an aluminium portion did not have a circularform, but had a rope form. That is, the microstructured material inwhich columns of the columnar structured material of aluminium wereuniformly dispersed within a silicon region could not be obtained.Further, the size was far larger than 10 nm. Also, when the section wasobserved by FE-SEM, the width of the aluminium portion exceeded 15 nm.Note that the aluminium/silicon mixture film thus obtained was subjectedto analysis of the fractional amount (atomic %) of silicon with respectto the total amount of aluminium and silicon by ICP (induction-coupledplasma emission spectrometry). As a result, the fractional amount ofsilicon with respect to the total amount of aluminium and silicon was 15atomic %.

Further, as a comparative sample B, the aluminium/silicon mixture filmcontaining 75 atomic % of silicon with respect to the total amount ofaluminium and silicon was formed on the glass substrate into a thicknessof approximately 200 nm by sputtering. Used as the target was the 4-inchaluminium target on which fourteen silicon chips 13 of 15 mm square weresuperposed. The sputtering conditions were set such that the RF powersupply was used, an Ar flow rate of 50 sccm, a discharge pressure of 0.7Pa, and a starting power of 1 kW. Also, the temperature of the substratewas set to the room temperature.

The comparative sample B was observed by FE-SEM (field emission scanningelectron microscope). In the sample surface viewed from right above thesubstrate, the aluminium portion could not be observed. Also, even whenthe section was observed by FE-SEM, the aluminium portion could not beobserved clearly. Note that the aluminium/silicon mixture film thusobtained was subjected to analysis of the fractional amount (atomic %)of silicon with respect to the total amount of aluminium and silicon byICP (induction-coupled plasma emission spectrometry). As a result, thefractional amount of silicon with respect to the total amount ofaluminium and silicon was 75 atomic %.

Further, samples were each prepared only by changing the condition ofthe number of the silicon chips compared to the case of producing thecomparative sample A such that the proportions of silicon with respectto the total amount of the aluminium/silicon mixture were respectively20 atomic %, 35 atomic %, 50 atomic %, 60 atomic %, and 70 atomic %. Thefollowing table shows the case where the microstructured material inwhich columns of the columnar structured material of aluminium wereuniformly dispersed within a silicon region was obtained, which isrepresented by “Yes”, and the case where the microstructured materialwas not obtained, which is represented by “No”.

TABLE 1 Proportion of Silicon (atomic %) Microstructured Material 15(Comparative Example A) No 20 Yes 25 Yes 35 Yes 50 Yes 55 Yes 60 Yes 65Yes 70 Yes 75 (Comparative Example B) No

Accordingly, the content of silicon with respect to the total amount ofaluminium and silicon was adjusted to a range from 20 atomic % to 70atomic %, thereby making it possible to control the hole diameter of theproduced aluminium nanostructured material and to produce the aluminiummicrowire superior in linearity. Note that for observation of thestructure, TEM (transmission electron microscope) or the like may beutilized in addition to SEM. Note that the above-mentioned content wasthe same even when using germanium or the mixture of silicon andgermanium instead of silicon described above.

Further, as a comparative sample C, the aluminium/silicon mixture filmcontaining 55 atomic % of silicon with respect to the total amount ofaluminium and silicon was formed on the glass substrate into a thicknessof approximately 200 nm by sputtering. Used as the target was the 4-inchaluminium target on which eight silicon chips 13 of 15 mm square weresuperposed. The sputtering conditions were set such that the RF powersupply was used, an Ar flow rate of 50 sccm, a discharge pressure of 0.7Pa, and a starting power of 1 kW. Also, the temperature of the substratewas set to 250° C.

The comparative sample C was observed by FE-SEM (field emission scanningelectron microscope). In the sample surface viewed from right above thesubstrate, the boundary between aluminium and silicon could not beobserved clearly. That is, the aluminium nanostructured material couldnot be observed. In other words, under the substrate temperature beingtoo high, the state became more stable, so that it was assumed that thefilm growth for forming the aluminium nanostructured material cannot beattained.

Note that in order to obtain the structured material in which thecolumnar members are dispersed, it is also a preferable form that thecomposition of the target is set as Al:Si=55:45 or the like.

Example 2

This Example is an example in which a porous film made of silicon oxidewas formed using aluminium and silicon as substances forming eutectictogether, a pattern of dots made of gold was formed using the porousfilm, and a substrate made of GaAs that is a typical semiconductormaterial was etched to form a GaAs columnar structured material having avery minute structure.

In this example, a GaAs substrate was used as a substrate. A descriptionwill hereinbelow be given with respect to a method of forming a porousfilm made of silicon on this substrate.

First, a mixed film made of aluminium and silicon having a filmthickness of 100 nm was formed on the substrate. Used as the target wasa 4-inch aluminium target on which six silicon chips of 15 mm squarewere superposed. Sputtering was carried out using RF power supply underthe conditions of: Ar flow rate of 50 sccm; a discharge pressure of 0.7Pa; and a starting power of 300 W. Also, a temperature of the substratewas set to the room temperature.

Here, as the target, one having six silicon chips arranged on analuminium target was used. However, the number of the silicon chips isnot limited thereto because it varies according to the sputteringconditions, and it may be such that a desired structure can be formedhaving aluminium columns dispersed in silicon, as described below. Inaddition, the target is not limited to one having silicon chips arrangedon an aluminium target, and it may be one having aluminium chipsarranged on a silicon target, or a target obtained by sintering siliconand aluminium powders may be used.

Further, the RF sputtering was used as a sputtering method in thisexample, but it is not limited thereto; it may be an ECR sputteringmethod, a DC sputtering method, or an ion beam sputtering method.Further, the sputtering conditions depend on an apparatus and are notlimited to the conditions described above. In addition, even among vapordeposition methods other than the sputtering method, any methods withwhich a desired structure can be formed may be applied to the presentinvention.

The aluminium-silicon mixture film obtained in this way was analyzedconcerning the fractional amount of silicon (atomic %) with respect to atotal amount of aluminium and silicon through ICP (induction-coupledplasma emission spectrometry). As a result, it was found that thefractional amount of silicon was about 37 atomic % with respect to thetotal amount of aluminium and silicon.

Further, the aluminium-silicon mixture film produced as described abovewas observed with the field emission scanning electron microscope(FE-SEM). It was observed that substantially circular minute aluminiumcolumns surrounded by silicon material were arranged two-dimensionally.The average hole diameter 2r of the aluminium column parts, which wasfound through image processing, was 5 nm, and the averagecenter-to-center interval 2R thereof was 10 nm. In addition, when thecross section thereof was observed with the FE-SEM, a height L of thefilm was 100 nm, and the respective aluminium column parts wereindependent of each other.

In addition, when this thin film sample was analyzed through the X-raydiffraction method, a diffraction line of silicon was not confirmed, andit was understood that the silicon was amorphous. On the other hand, aplurality of diffraction lines of aluminium were confirmed, and it wastherefore understood that aluminium was polycrystalline.

Based on the above, production of the aluminium-silicon structuredmaterial was confirmed which contains crystalline aluminium columnswhose vicinities were surrounded by amorphous silicon and which have anaverage diameter 5 nm and an average height of 100 nm.

Next, this aluminium-silicon structured material obtained as describedabove was immersed in 98% sulfuric acid, and etching was selectivelyperformed for the aluminium columnar structure parts to form microholes.As a result of the observation with the FE-SEM for the film after theetching, it was confirmed that only the aluminium columns were removed,and the film became porous. It was understood that the shape of thesilicon part was not substantially changed as compared with its statebefore the aluminium removal. In this case as well, when the crosssection thereof was observed with the FE-SEM, it became apparent thataluminium was completely removed up to the substrate interface. Byfollowing the above steps, the porous silicon film having on thesubstrate the through holes perpendicular to the substrate could beproduced.

Next, a description will now be given with respect to a method ofintroducing gold into the formed porous film to form a dot pattern.

First of all, the silicon porous film formed through the above-mentionedprocesses was dipped in a commercial electroplating liquid (anelectroplating liquid for gold manufactured by KOJUNDO CHEMICALLABORATORY. CO. LTD., a trade code K-24E), and the electrodeposition wascarried out in an acid bath (pH=4.5) having a temperature held at 40° C.at a current density of 0.5 A/dm².

The film after being subjected to the gold electrodeposition was rinsedwith pure water, and thereafter the surface and the cross sectionthereof were observed with the FE-SEM. As a result, it was confirmedthat gold was introduced into the microholes uniformly, and a minutecolumnar structure was formed.

This film was dipped in a 30% aqueous solution of sodium hydroxide toremove silicon present in the periphery of gold. This processing usingthe aqueous solution of sodium hydroxide offers the effect as well ofremoving an oxide layer present on the surface of the GaAs substrate toclean the surface of the GaAs substrate. The substrate after completionof the removal of silicon was observed with an FE-SEM, and as a result,it was confirmed that the minute columnar portions of the columnarstructured material made of gold were arranged with high density on thesurface of the substrate to form the pattern of dots made of gold. Anaverage diameter 2r′, an average center-to-center interval 2R′ and aheight L′ of the gold columnar structured material which were obtainedthrough the image processing were 5 nm, 10 nm, and 10 nm, respectively.

Next, the substrate having the dot pattern formed thereon wasselectively etched. The etching was carried out by utilizing a reactiveion beam etching method (RIBE). But, if the RIBE method was used, thenthe surface of the GaAs substrate may be damaged due to the acceleratedions struck against the surface of the GaAs substrate in some cases. Insuch cases, as will be described later, it is preferable to subject thesubstrate to an annealing treatment.

After completion of the above-mentioned etching process, the substratewas dipped in an aqueous solution of (Na₂SO₄, C₆FeK₃N₆, and H₂NCSNH₂) toremove the pattern of dots made of gold.

Moreover, the substrate was installed in the ambient atmosphere rich inAs, and the temperature of the substrate was then raised up to 580° C.to anneal the substrate to thereby carry out recrystallization.

When the substrate obtained through the above-mentioned process wasobserved with a transmission electron microscope (TEM), it was observedthat microstructured columnar portions made of GaAs were arranged on thesubstrate, and hence it was confirmed that a columnar-structuredmaterial was formed. A diameter and a height of the columnar structuredmaterial roughly estimated from the observed TEM image were 4 nm, and 20nm, respectively, and a center-to-center interval of the columnarstructured material was 10 nm.

Consequently, according to this example, it was confirmed that the dotpattern was formed from the above-mentioned porous film to be used asthe mask, whereby a plurality of columnar portions of the columnarstructured material made of GaAs having the extremely minute structurecould be simultaneously formed at the minute intervals.

Example 3

In this example, a porous film made of germanium was formed usingaluminium and germanium as substances forming eutectic together, apattern of dots made of gold was formed using the porous film, and asubstrate having a multiple quantum well structure made of GaAs/InGaAsformed thereon was selectively etched to form a columnar structuredmaterial made of GaAs/InGaAs. When an application to an optical device,an electronic device or the like is considered, a minute columnarstructured material made of a plurality of semiconductor layers is veryuseful.

In this example, as shown in FIG. 5A, a columnar structured materialformation layer 55 made of GaAs/InGaAs (a first GaAs layer 51, an InGaAslayer 52, and a second GaAs layer 53) was formed on a base substrate 54to be used as a substrate. A description will hereinbelow be given withrespect to a method of forming a porous film made of germanium on thissubstrate.

First, a mixed film made of aluminium and germanium having a filmthickness of 200 nm was formed. Used as the target was a 4-inchaluminium target on which four germanium chips of 15 mm square weresuperposed. Sputtering was carried out using RF power supply under theconditions of: Ar flow rate of 50 sccm; a discharge pressure of 0.7 Pa;and a starting power of 1 kW. Also, a temperature of the substrate wasset to the room temperature.

Here, as the target, one having four germanium chips arranged on analuminium target was used. However, the number of the germanium chips isnot limited thereto because it varies according to the sputteringconditions, and it may be such that a desired structure can be formedhaving aluminium columns dispersed in germanium, as described below. Inaddition, the target is not limited to one having germanium chipsarranged on an aluminium target, and it may be one having aluminiumchips arranged on a germanium target, or a target obtained by sinteringgermanium and aluminium powders may be used.

Further, the RF sputtering was used as a sputtering method here, but itis not limited thereto; it may be an ECR sputtering method, a DCsputtering method, or an ion beam sputtering method. Further, thesputtering conditions depend on an apparatus and are not limited to theconditions described above. In addition, even among vapor depositionmethods other than the sputtering method, any methods with which adesired structure can be formed may be applied to the present invention.

Next, the aluminium-germanium mixture film obtained in this way wasanalyzed concerning the fractional amount of germanium (atomic %) withrespect to the total amount of aluminium and germanium through ICP(induction-coupled plasma emission-spectrometry). As a result, it wasfound that the fractional amount of germanium was about 37 atomic % withrespect to the total amount of aluminium and germanium.

The aluminium-germanium mixture film produced as described above wasobserved with the field emission scanning electron microscope (FE-SEM).It was observed that substantially circular minute aluminium columnssurrounded by germanium material were arranged two-dimensionally. Theaverage hole diameter 2r of the aluminium column parts, which was foundthrough image processing was 10 nm, and the average center-to-centerinterval 2R thereof was 15 nm. In addition, when the cross sectionthereof was observed with the FE-SEM, the height L of the film was 100nm, and the respective aluminium column parts were independent of eachother.

In addition, when this thin film sample was analyzed through the X-raydiffraction method, a diffraction line of germanium was not confirmed,and it was understood that germanium was amorphous. On the other hand, aplurality of diffraction lines of aluminium were confirmed, and it wastherefore understood that aluminium was polycrystalline.

Based on the above, production of the aluminium-germanium structuredmaterial was confirmed which contains crystalline aluminium columnswhose vicinities were surrounded by amorphous germanium and which havethe diameter 2r of 10 nm, the interval 2R of 15 nm, and the height L of100 nm.

This aluminium-germanium structured material was immersed in 98%sulfuric acid (dense sulfuric acid), and etching was selectivelyperformed for the aluminium columnar structure parts to form microholes.

As a result of the observation with the FE-SEM for the film after theetching, it was confirmed that only the aluminium columns were removed,and the film became porous. It was understood that the shape of thegermanium part was not substantially changed as compared with its statebefore the aluminium removal. In this case as well, when the crosssection thereof was observed with the FE-SEM, it became apparent thataluminium was completely removed up to the substrate interface. Byfollowing the above steps, the porous germanium film having on thesubstrate the through holes perpendicular to the substrate could beproduced.

Next; a description will now be given with respect to a method ofintroducing gold into the formed porous film to form a dot pattern.

First of all, the germanium porous film formed through theabove-mentioned processes was dipped in a commercial electroplatingliquid (an electroplating liquid for gold manufactured by KOJUNDOCHEMICAL LABORATORY. CO. LTD., a trade code K-24E), and theelectrodeposition was carried out in an acid bath (pH=4.5) having atemperature held at 40° C. at a current density of 0.5 A/dm².

The film after being subjected to the gold electrodeposition was rinsedwith pure water, and thereafter the surface and the cross sectionthereof were observed with the FE-SEM. As a result, it was confirmedthat gold was introduced into the microholes uniformly, and a columnarstructure was formed.

This film was dipped in a 50% aqueous solution of nitric acid to removegermanium present in the periphery of gold. The substrate aftercompletion of the removal of germanium was observed with an FE-SEM, andas a result, it was confirmed that the minute columnar portions of thecolumnar structured material made of gold were arranged with highdensity on the surface of the substrate to form the pattern of dots madeof gold. The average diameter 2r′ and the average center-to-centerinterval 2R of the gold columnar structured material obtained on thebasis of the image processing were 10 nm and 15 nm, respectively.

Next, the substrate having the dot pattern formed thereon wasselectively etched. The etching was carried out by utilizing a reactiveion beam etching method (RIBE). But, if the RIBE method is used, thenthe surface of the GaAs substrate may be damaged due to the acceleratedions struck against the surface of the GaAs substrate in some cases. Insuch cases, as will be described later, it is preferable to subject thesubstrate to an annealing treatment.

After completion of the above-mentioned etching process, the substratewas dipped in an aqueous solution of (Na₂SO₄, C₆FeK₃N₆, and H₂NCSNH₂) toremove the pattern of dots made of gold.

Moreover, the substrate was installed in the ambient atmosphere rich inAs, and the temperature of the substrate was then raised up to 580° C.to anneal the substrate to thereby carry out recrystallization.

When the substrate obtained through the above-mentioned processes wasobserved with a transmission electron microscope (TEM), it was observedthat columnar portions of a columnar structured material 56 (including afirst GaAs layer 57, an InGaAs layer 58, and a second GaAs layer 59)made of GaAs/InGaAs as shown in FIG. 5B were arranged on the surface ofthe substrate 54, and it was also confirmed that the minute columnarstructured material 56 was formed. The diameter and height of each dotroughly estimated from the observed image were 8 nm and 60 nm,respectively, and the dots were arranged at center-to-center intervalsof 15 nm.

Consequently, according to this example, it was confirmed that the dotpattern was formed from the above-mentioned porous film to be used asthe mask, whereby a plurality of columnar portions of the columnarstructured material made of GaAs/InGaAs having the extremely minutestructure could be simultaneously formed at the minute intervals.

As set forth hereinabove, according to the present invention, thepattern of the minute dots is formed using the novel porous film inwhich the microhole diameter of each microhole is extremely minute, andthe microholes are arranged at extremely minute intervals, and thecolumnar structured material having the extremely minute structure canbe formed so as to be densely arranged with the dot pattern used as theetching mask. In addition, if the columnar structured material accordingto the present invention is applied to a semiconductor laser forexample, then it is possible to realize the promotion of highperformance such as reduction of a threshold current, stabilization ofcharacteristics, and enhancement of a gain. Moreover, it is to beunderstood that the present invention can also be applied tomanufacturing of electronic devices such as an operational element, andan optical device both utilizing the effect of closing the electrons orlight and the quantum effect.

1. A method of manufacturing a dot pattern, comprising the steps of:preparing a structured material composed of a plurality of columnarmembers containing a first component and a region containing a secondcomponent different from the first component surrounding the columnarmembers, the structured material being formed by depositing the firstcomponent and the second component on a substrate; removing the columnarmembers from the structured material to form a porous material having acolumnar hole; introducing a material into the columnar hole portions ofthe porous material to form a dot pattern; and removing the porousmaterial.
 2. The method of manufacturing a dot pattern according toclaim 1, wherein the second component is contained at a ratio of notless than 20 atomic % and not more than 70 atomic % with respect to thetotal amount of the first component and the second component.
 3. Amethod of manufacturing a columnar structured material using a dotpattern manufactured by the method according to claim 1, comprising: astep of etching the substrate with the dot pattern as a mask; and a stepof removing the dot pattern.
 4. The method of manufacturing a dotpattern according to claim 1, wherein the removing step of removing thecolumnar members is an etching step.
 5. The method of manufacturing adot pattern according to claim 1, wherein the introducing step ofintroducing the material into the holes is an electrodeposition step. 6.The method of manufacturing a columnar structured material according toclaim 3, wherein the step of etching the substrate with the dot patternas a mask is a dry etching step.
 7. The method of manufacturing a dotpattern according to claim 1, wherein the material contains a noblemetal.
 8. The method of manufacturing a dot pattern according to claim1, wherein the first component and the second component form a eutecticsystem.
 9. The method of manufacturing a dot pattern according to claim1, wherein the second component is contained at a ratio of not less than30 atomic % and not more than 60 atomic % with respect to the totalamount of the first component and the second component.
 10. The methodof manufacturing a dot pattern according to claim 1, wherein theplurality of columnar members are crystalline aluminum columns.
 11. Themethod of manufacturing a dot pattern according to claim 1, wherein theregion is composed of an amorphous Si_(x)Ge_(1-x), with 0<x<1.
 12. Themethod of manufacturing a dot pattern according to claim 1, wherein thedeposition of the first component and the second component is performedby a sputtering method.
 13. The method of manufacturing a dot patternaccording to claim 1, wherein the material contains a silicon oxide. 14.The method of manufacturing a dot pattern according to claim 1, whereinthe material contains a silicon nitride.
 15. The method of manufacturinga dot pattern according to claim 1, wherein the material contains anorganic substance.